The present invention relates to a method of determining radioactive nuclides by obtaining time interval of pulses incident to an α-ray detector and analyzing it.
In the measurement of radioactivity, pulse-height discrimination of radiations (the energy incident to a radiation detector) is carried out and, by the comparison with a previously prepared energy library, the identification of a radioactive nuclide is carried out. However, under the environment wherein plural radioactive nuclides exist and when the energies of the nuclides are close to each other, they cannot be discriminated, whereby it is necessary to carry out a chemical separation.
For example, when an abnormal-leakage accident occurs in nuclear facilities, there is a possibility that an α-ray releasing nuclide having a long half-life, such as plutonium, etc., contained in the nuclear fuel is released in the environment. Thus, it is necessary to quickly determine plutonium in the suspended dust in the atmosphere. Practically, by sucking the air by a pump, the suspended dust in the air is collected on a filter and after recovering the dust filter, the dust is measured by an α-ray detector (for example, a silicon surface barrier semiconductor detector) and a pulse-height discrimination is carried out.
However, in this case, radon (Rn), polonium (Po), lead (Pb), bismuth (Bi), etc., which are the disintegrated products of uranium (U) and thorium (Th) largely existing in nature are detected as the predominant nuclides and plutonium (Pu) and the like are concealed in the background. Accordingly, it is necessary that, prior to the α-ray measurement by a silicon semiconductor detector, the recovered dust filter is subjected to a pre-treatment in which the dust filter is wholly decomposed with nitric acid and hydrofluoric acid and then plutonium is isolated by an anionic exchange method.
Because such a chemical separation is indispensable in the prior art techniques, a complicated operation is required, and a quick determination cannot be carried out. Incidentally, for the analysis of plutonium in the suspended dust in the atmosphere described above, the time of about one week is required for the determination thereof.